The present invention relates to an apparatus and method for correcting spinal deformities such as scoliosis and kyphosis, and for internal fixation of the spine.
Spinal deformities of interest here are chiefly characterized by geometric deviation of the spinal column from that of the normal configuration as well as spinal instabilities. For example, scoliosis is a lateral deviation of the spinal column from the essentially normal straight line configuration as viewed from the ventral or dorsal of the spinal column. When these abnormal spinal curvatures exceed certain limits correction by surgical treatment must be considered. The surgical treatment for such conditions is known as arthrodesis and involves both the correction of the curvature of the spine in the region of deviation to the maximum possible extent and also the fusion by autogenous bone grafts of the vertebrae in the region of abnormal curvature. Correction of the spinal configuration can be attempted prior to surgical treatment by continuous traction of the spine or by corrective plaster casts. However, a corrected and fixed configuration of the vertebrae must be maintained during the period in which vertebrae are being fused so that the deformity is corrected by the final fusion.
A known surgical technique for maintaining corrected positioning of vertebrae during the fusion process involves the attachment, by hooks, of rods to the spine. The rods are used to apply forces to straighten the spine and to maintain the corrected configuration until the vertebrae are fused. Hooks and a threaded rod are attached to the dorsal or posterior elements of vertebrae of the spine on the convex side of the deformity such that compression can be applied to the vertebrae and thus correct the spinal configuration. Hooks with a second rod are also attached to the laminae on the concave side of the deformity to provide distraction by the reverse application of force as is provided by the compression system of hooks and threaded rod on the convex side of the deformity. Such systems of hooks and rods is known as Harrington instrumentation. Harrington type instrumentation is disclosed in U.S. Pat. Nos. 4,269,178; 4,274,401; 4,361,141; 4,369,769; 4,369,770; 4,382,438; 4,386,603; 4,404,967; 4,409,968; 4,411,259; and, 4,422,451.
Another known surgical technique for maintaining corrected positioning of vertebrae during arthrodesis involves attachment by screws or staples to the ventral or anterior of vertebrae on the convex side of the deformity, and the interconnection of the stapled vertebrae by passing a cable, such as braided titanium wire, through holes in the heads of the screws affixing the staples to the vertebrae. Then starting at one end, pairs of stapled vertebrae are compressed by applying tension to the cable to straighten the curve. Compression between vertebrae is maintained by crimping the screw-heads into the cable. This system of staples, screws, and cable is known as Dwyer instrumentation.
Though the Harrington and Dwyer instrumentation systems have predominantly been independently used for treatment of deformed spines, they have been also used in combination for the treatment of patients with painful adult idiopathic scoliosis. First the Dwyer procedure was used in this combination treatment, and later the Harrington procedure was performed. This combined use of Harrington and Dwyer instrumentation on patients is outlined in more detail in the article "Combined Dwyer and Harrington Instrumentation and Fusion in the Treatment of Selected Patients With Painful Adult Idiopathic Scoliosis", Spring, June, 1978, pp. 135-141.
A third known surgical technique for maintaining corrected positioning of vertebrae during the fusion process involves the attachment, by wires, of rods to the spine. The rods are used for support to straighten the spine, and also to maintain the corrected configuration until the vertebrae are fused. To attach the rods to the spine, wires are passed about the laminae on each of the two posterior sides of each vertebra to which the rods are to be attached. Then beginning on the convex side of the deformation, a first rod is positioned adjacent the spinous processes of the vertebrae at one end of the line of vertebrae to be attached, and the wires on that side of the vertibrae are twisted about the rod to attach it to the vertebrae. Progressing along the line of vertebrae, the spinal column is levered against the rod and wires mounted about each vertebra are twisted about the rod to maintain the spinous processes on the convex side of the deformation adjacent the rod. This attachment of vertebrae to the rod corrects the spinal deformity. A second rod to augment the strength of the instrumentation is then placed adjacent the other side of the spinous processes from the first rod, and the wires mounted about the laminae on the side of the vertebrae adjacent the second rod are twisted about the second rod to maintain it in a support position against the vertebrae. This system of rods and wires is known as Luque spinal instrumentation.